1. Field of the Invention
The present invention relates to bag filling methods, and more specifically to a method of simultaneously forming and filling bags formed from multi-substrate sheets or webs. The sheets include strips of a polymeric film and a ventilating polymeric mesh connected to one another along a longitudinal seam. The bags are filled to a method of simultaneously forming and filling using a vertical form, fill and seal machine and to the sheet used to form the bag.
2. Discussion of the Related Art
Fruits, vegetables, and other items are often stored and sold in bags in order to offer a number of the items for sale in a single prepackaged configuration. The typical bag is also intended for point-of-purchase use and, therefore, also serves as a marketing material for its contents. It is therefore desirable to configure a bag such that its contents can be viewed by prospective purchasers without opening the bag. A plastic film is ideal for this purpose because it is transparent. It also can easily receive printed indicia that may identify the items, their source, and/or other information. Separate printed labels are also easily adhered to plastic film bags. Because a plastic film is flexible, low cost, and easily heat sealed to itself and other materials, plastic film bags can be manufactured and filled relatively easily and inexpensively.
However, traditional plastic films such as low density polyethylene (LDPE) have relatively low gas permeability. They are therefore poorly suited for storing items that must be exposed to the ambient air or “breathe” in order to prevent premature spoilage. For this reason, many produce items, such as apples, onions, and oranges, were traditionally stored and sold in bags from a woven or knit mesh material, such as a polymeric mesh material, that provides sufficient ventilation to prevent premature spoilage of the produce items contained in the bag. The polymeric mesh allows sufficient air to flow into and out of the bag to properly ventilate the produce contained within the bag and prevent spoilage. The bags are normally formed to have polymeric film strips attached across the top of the bag to form a more reliable seal for the bag and prevent premature opening of the bag, as well as to provide a surface on which printed matter can be located on the bag.
Mesh bags have disadvantages, however. The items stored in the bags cannot be easily seen by prospective purchasers. The side and bottom seams of the bags also tend to be relatively weak because the seams do not contain enough material to strongly bond the edges to one another. Indicia also cannot be easily printed directly onto the mesh material. It is therefore necessary in many instances to apply separate polymeric film strips to ends and/or sides of the bag to reinforce the seam and enclose the bag. A separate film strip may also need to be applied to one side of an all-mesh bag for the purposes of receiving the desired display indicia. However, this separate strip actually hinders the viewing of items in the bag. It also adds to the cost of the bag because it requires an additional manufacturing step for its application or at least the provision of an additional strip-applying station on a bag making machine. A bag having these characteristics is disclosed in Antonacci et al. U.S. Pat. No. 5,823,683, the subject matter of which is incorporated by reference.
Many of the problems addressed above are overcome by so-called “half-and-half” bags. A half-and-half bag has a front panel or “half” formed from a polymeric film and a rear panel or “half” formed from a polymeric mesh material. The mesh half provides ample ventilation for the stored items. The film half can receive printed indicia and also can be easily heat bonded to other film materials. The film material can also be securely heat bonded to itself and to the mesh material. Hence, half-and-half bags combine the advantages of all mesh bags and all film bags.
Half-and half bags are formed in a continuous bag making machine from a pair of sheets formed from a polymeric mesh and a polymeric film, respectively. The sheets are unwound from respective rolls and fed concurrently through a bag making machine in an overlying relationship, where they are heat-bonded to one another at their mating edges. The sheets are then folded over while other strips of the polymeric film are attached to the sheets at appropriate locations. The sheets are then cut into longitudinal strips and sealed at the bottom edge to form an open-topped bag. After the bags are completed, they are shipped to a supplier, who fills the bags with items and closes the bags, often by heat sealing the tops using a sealing strip formed from an extension of the film panel. A half and half bag of this general type is disclosed, e.g, in Fox et al. U.S. Pat. No. 6,024,489, which is herein incorporated by reference. A machine and method for producing a bag of this general type is commercially available from Hudson Sharp.
Of course, making and filling bags in two steps using two different machines adds considerable cost to the end product. In an attempt to reduce this cost, it is also known in the prior art to form a bag from a continuous sheet, fill it with items, and seal its side and bottom edges—all in one operation using a so-called “form, fill, and seal” machine. One such machine and its method of operation are described in Pelster et al. U.S. Pat. No. 4,091,595, incorporated herein by reference. In the Pelster et al. '595 patent, a sheet or net of a polymeric netting is pulled over a hollow tube to form a sleeve, and the bottom of the sleeve is sealed and filled with a number of items. The bottom of the sleeve is then indexed down beneath the tube. The top of the thus-formed bag is then sealed to form a filled polymeric mesh bags. The cost of forming and filling such a bag is considerably less than the combined costs of forming and filling more traditional net bags. However, the resulting bag has all of the disadvantages of a traditional mesh bag, including lack of an indicia-receiving surface and relatively weak seams. Thus, any labeling that is to be placed on the bag must be placed on the bag after sealing of the bag, or on a lower closure that is separately applied to the bag during sealing in order to form a lower seal for the bag in a manner similar to the other prior art mesh bags discussed previously.
Therefore, it is desirable to develop a method of forming and filling bags using a low cost bag material which is preformed of continuous sheet or web containing one or more strips of a polymeric mesh material and a number of strips of a polymeric film or labeling material. The web should be one that can be converted in a continuous form, fill and seal machine to form a filled bag for sale to a consumer immediately after removal from the machine. It is also desirable that the web be capable of forming a bag that has sufficient seam strength to securely retain a number of items within the bag, even during rough handling of the bag.